The global incidence of drug resistant TB (Mycobacterium tuberculosis), particularly multi-drug resistant (MDR) and extremely-drug resistant (XDR) strains, is a major worldwide issue. Rates of MDR TB have been estimated to be 4.8% of the estimated 9.8 million TB infections, but rates as high as 55% have been observed for previously treated patients. TB can be effectively treated if properly identified. However, delayed initiation of appropriate treatment in suspected MDR-TB cases is associated with excess morbidity and nosocomial transmission.
It has been determined that the main contributor to delay in treatment is poor sensitivity of diagnostic tests; the average sensitivity of sputum microscopy is <60% in immunocompetent patients and is lower in HIV infected cases. Frequent smear-negative disease increases the difficulty with detecting HIV-associated TB as well. While mycobacterium culture is much more sensitive, it has a very slow turnaround time of 2-8 weeks and is technically complex. Nucleic acid amplification-based tests have improved detection sensitivity and time-to-result but historically have been difficult to effectively implement. A recently described real-time PCR approach brings ease-of-use but at high cost.